Fuse construction



Patented June 10, 1941 FUSE CONSTRUCTION Sigurd l. Llndell and Anthony Van Ryan, Chicage, 11]., asslgnors to Schweitzer a Conrad, Inc., Chicago, 11]., a corporation of Delaware Application December 28, 1939, Serial No. 311,337

17 Claims.

This invention relates, generally, to circuit interrupting apparatus and it has particular relation to fuse links.

The present invention is particularly related to fuse links for connection on the secondary side of a distribution transformer where the normal load current is variable and may be relatively high while the voltage is relatively low, i. e., of the order of 110 or 220 volts. The type of fuse link disclosed herein constitutes in itself a complete circuit interrupting device and requires no additional housing or other support means.

An object of this invention is to protect the fusible element of a secondary fuse link from the weather and at the same time avoid the generation of destructive pressure on blowing of the fusible element.

Still another object of this invention is to prevent dangling of the flexible leads of a secondary fuse link after it has blown.

A further object of this invention is to provide for indicating that a secondary fuse link has blown and still prevent dangling of the flexible leads.

A still further object of this invention is to seal the ends of the outside insulating sleeve of a secondary fuse link against the entrance of moisture.

Still another object of the invention is to permit movement of a terminal of a fuse link from one position to another and to seal it with respect to its housing in either position.

Other objects of this invention will, in part, be obvious and in part appear hereinafter.

Accordingly the invention is disclosed in the embodiments thereof shown in the accompanying drawings, and it comprises the features of construction, combination of elements and arrangement of parts which will be exemplified in the constructions hereinafter set forth, and the scope of the application of which will be indicated in the appended claims.

For a more complete understanding of the nature and scope of this invention, reference may be had to the following detailed description taken in connection with the accompanying drawings, in which:

Figure l is a view showing how the secondary fuse link of the present invention can be installed Figure 2, but illustrating the condition of the secondary fuse link after it has blown;

Figure 4 is a view, similar to that shown in Figure 2, but in which the fusible element comprises a coil of silver wire; and

Figure 5 is a view, similar to that shown in Figure 2, but illustrating certain modifications in the details of construction.

Referring first to Figure 1 of the drawings, it will be observed that the reference characters It and II designate line conductors that may be mechanically interconnected by a suitable insulator l2 which electrically insulates them from each other. The conductor ill may be connected to one terminal of the secondary winding of a distribution transformer while the other conductor Il may be connected to one terminal of the load. The conductors l0 and II are electrically interconnected by means of a secondary fuse link, shown generally at ii, the details of construction of which will be presently set forth. The secondary fuse link i3 is provided with flexible leads i4 and I! that may be connected to the conductors Ill and II, respectively, by any suitable connectors.

In Figure 2 of the drawings the details of construction of one embodiment of the fuse link H are shown. Since the fuse link I! constitutes the sole apparatus that is employed for interrupting the circuit and since no housing is provided therefor, it must be suitably weatherproofed since it is directly exposed to the elements.

In order to protect the secondary fuse link H from the weather it is provided with an outer sleeve I9 of insulating material that is capable of resisting the elements. The sleeve i9 is prefcrably formed of a phenolic condensation product although, if desired, it can be formed of glass or porcelain, When the sleeve is formed of an organic material such as a phenolic condensation product, relatively high pressure is likely to be generated within it due to the heat of the arc formed on blowing of the link if the arc is permitted to contact the interior surface thereof. As will be hereinafter set forth, a two part inner sleeve is provided and formed of relatively inert material for preventing the are from contacting the inner surface of the outer sleeve l9.

Within the sleeve I! there are provided two relatively infusible terminals 20 and 2|. The terminal 20 is movable relative to the sleeve I! while the terminal 2| is fastened thereto. The terminals 20 and 2| are provided with tubular end portion 22 and 22 extending toward each other. These tubular end portions are deformed on to the ends of a strain element 24 which usually takes the form of a high strength wire and may be formed of a high strength alloy such as nickel chromium alloy. When the tubular end portions 22 and 23 are deformed, seml-circular sockets are provided for receiving the ends of a fusible element 25 which may be in the form of a short length of tin wire. The diameter of the fusible element '25 will of course vary depending upon the rating oi the fuse link.

The ils of the arrangement of the strain and fusible elements 24 and 25, Just described, are more fully set forth in Patent No. 2,174,767. Instead of employing tin alone for the fusible element 25, the composite fusible element, comprisin a silver sheath and a tin core, disclosed in the application of Triplett, Serial No. 144,789, filed May 26, 1937, can be employed.

It will be observed that the flexible leads l4 and I5 are connected to the terminals and 2|, respectively, by being inserted in tubular end portions 26 and 21 thereof. The end portions 25 and 21 are suitably deformed and swaged in order to provide the desired electrical connection without requiring the use of solder.

It will also be observed that the flexible lead l5 extends from the terminal 2| out of the outer sleeve I!) through a retainer member 30. The retainer member is provided with a tubular portion 3| which, as shown, is deformed onto the flexible lead IS. The retainer member 3|! is secured to the outer sleeve I9 by a ferrule 32 which has a lip 33 that is turned or crimped into a groove 34 on the retainer member 30. The ferrule 32 is securely fastened to the sleeve l9 by having the portion 35 thereof crimped into a suitable groove in the outer surface of the sleeve IS. The ferrule 32 serves to hold the retainer member 30 tightly against the one end of the sleeve l9 and together they provide an effective seal against the entrance of moisture.

As previously indicated, the terminal 20 is movable relative to the sleeve |9. Such movement is desired in order to separate the terminals 20 and 2| when the strain and fusible elements 24 and 25 blow in order to assist in interrupting the arc which is then formed. While it b desirable to provide for some movement of the terminal 20 in order to interrupt the electrical circuit through the fuse link l3, it is undesirable to permit the terminal 20 to mechanically disengage the sleeve IS in the blown condition. If such action is permitted, then the flexible leads l4 and I5 will dangle from the line conductors l0 and N, Figure 1, and there is a likelihood that they may come into contact engagement with other conductors which obviously would be undesirable. However, it is desirable to permit movement of the terminal 20 not only sufflciently far to properly interrupt the circuit but also to provide by its movement to an alternate position an obvious indication that the fuse link has blown and that it' should be replaced.

The terminal 20 is provided with a tapered reduced portion 38 onto which one end of a metal tube 39 is crlmped. The other end of the metal tube 39 is expandedas indicated at 40 which provides a shoulder 4| that abuts a shoulder washer 42 that is held against the left hand end of the outer sleeve I! by a ferrule 43. As shown, one end 44 of the ferrule 43 is crimped over the shoulder washer 42 and a portion 45 is crimped into a suitable groove in the sleeve I! for holding it securely thereat.

An inner sleeve 40 of insulating material, pref- 5 erably of ceramic material, which may be purchased under the trade name "Steatite," is positioned in the expanded end portion 40 of the tube 39 and it is urged outwardly relative to the sleeve |9 by a coil compression spring 49 which reacts between the inner face of the retainer member 39 and a washer 50 which is located at the adjacent end of the inner sleeve 48. The sleeve 48 of ceramic material is coated with an arc extinguishlng medium, such as magnesium borate, boric acid, etc., which, by evolving water vapor, serves to protect the sleeve 48 from the heat that is generated by the strain and fusible elements 24 and 25 under normal operating conditions. Of course, it also assists in extinguishing the are that is formed on blowing of the strain and fusible elements 24 and 25.

It will be observed that the metal tube 39 and the inner sleeve 48 comprise a two part inner sleeve and, since they are formed respectively of metal and ceramic insulating material which are relatively inert inorganic materials, there is little likelihood of the generation of undesirable pressure within the sleeve I! on blowing of the strain and fusible elements 24 and 25 due to the heat of the resultant arc which would otherwise be the case if the inner surface of the sleeve I! were unprotected. Moreover, the relatively inert two part inner sleeve serves to protect the inner surface of the outer sleeve I! from the heat that is evolved from the fusible element 24 under normal operation. The water vapor that is evolved from the magnesium borate or boric acid coating assists in arc extinction. The metal that is fused and vaporized by the heat of the arc is rapidly cooled and condensed on the metal tube 39 and on the metallic terminals 20 and 2i.

With a view to providing a sealed connection between the sleeve l9 and the terminal 20, a

gasket 5| is provided in a groove 52 in the terminal 25. The gasket 5| is preferably formed of rubber and it engages the inner surface of the shoulder washer 42 which, as shown, is of relatively limited width. The purpose of this construction will be presently apparent.

In Figure 3 of the drawings the relative positions of the various parts are shown after the strain and fusible elements 24 and 25 have blown. As there illustrated, the terminal 20 has moved out of the sleeve l9 until the shoulder 4| of the metal tube 39 engages the shoulder washer 42. In this position the compression spring 49 moves the shoulder 4| fairly tightly against the shoulder washer 42 and thereby maintains a substantially sealed connection therebetween to prevent the entrance of moisture within the sleeve l9.

It will be observed that the gasket 5| engages only the relatively limited inner surface of the shoulder washer 42. Thus, as soon as the terminal 2. is moved outwardly sufliciently far for the gasket 5| to clear the shoulder washer 42, the terminal 25 is substantially free to move outwardly unhindered by the friction which previously existed between the gasket 5| and the inner surface of the shoulder washer 42.

In Figure 4 of the drawings the construction shown is substantially the same as that illustrated in Figure 2 and described hereinbefore. The terminals 20' and 2| are generally similar in construction to the terminals 20 and 2|. They are provided with end portions 22' and 23 extending toward each other which are tubular in form and which are deformed onto the ends of the strain and fusible elements 24' and 25'. In h s instance the strain wire 24 is the same as saunas the strain wire It described hereinbefore while the fusible element 2' is in the form of a coil of silver wire.

lnl 'igureliofthedrawingsitwillbeobeerved that the sleeve it is provided with relatively infusible terminals II and I, the former being movable relative to the sleeve ll while the latter is stationary. The terminals II and II are provided with tubular end portions facing each other which are deformed onto a strain element It and which provide semi-circular receptacles, as previously described, for a fusible element ll. Integraily formed with the stationary terminal ll is a tubular end portion 6! which is deformed onto the flexible lead II, as shown. The terminal, 51 is provided with a groove ll adjacent the deformed portion thereof in whichgis positioned a metal washer I that is held in place by a flange Ci of a ferrule t which has a portion ll crimped into a suitable groove in the sleeve It. Between the right hand end of the sleeve It and the inner face of the washer N there is provided a gasket in the form of a rubber.

washer which provides a sealed connection between the terminal and the sleeve II.

The movable terminal 68 is provided with a groove II in which one end of a metal tube II is crimped, as shown. The other end of the metal tube II is expanded as indicated at 12, thereby providing a shoulder 13 which is arranged to en gage a gasket 14, preferably formed of rubber, atthe left hand end of the sleeve ll. It will be understood that the engagement of the shoulder 13 with the gasket ll limits the outward movement of the terminal 86 when the strain and fusible elements it and I blow. The gasket I4 is held in place by a metal washer II which in turn is held in position by a flange ll of a ferrule 11 which has a portion it that is crimped into a suitable groove in the sleeve it.

It will be observed that the terminal 56 is provided with a tubular extension 1! that is deformed onto the flexible lead It for providing connection therebetween.

An inner sleeve ll of insulating material, pref erably formed of inert inorganic material such as porcelain or other ceramic material for the reasons stated hereinbefore, is provided in the expanded end I! of the metal tube II. A coil compression spring ll reacting against the gasket 60 and a washer II at the right hand end of the inner sleeve serves to bias the terminal 56 outwardly. As long as the strain and fusible elements 60 and ii remain unblown, the terminal 56 remains in the position shown in the drawings. The movement of the terminal it out of the sleeve I9 is arrested when the shoulder 13 engages t-he gasket 14. In the blown condition of the fuse link the inner sleeve I will be positioned substantially between the terminals l8 and 51 thereby increasing the insulation therebetween and providing a relatively great creepage distance over the inorganic insulating surface of'the ceramic sleeve It. This materially aids in extinguishing the arc formed on blowing of the strain and fusible elements 00 and ll and preventing its restriking after it has been extinguished. This is also characteristic of the fuse link constructions shown in Figures 2 and 4 of the drawings.

The gaskets l4 and it provide sealed connections between the terminals It and U, respectively, and the adjacent ends of the sleeve It so that the entrance of moisture is prevented. This is the case in either the blown or the unblown condition of the fuse link. In the blown condition the gasket It, as previously described, engases the shoulder 13 of the metal tube II and thereby continues the sealed connection. However, the construction shown in Figure 5 is somewhat less desirable than that shown in Figures 2 and 4 with respect to the sealing of the movable terminal to the outer protecting sleeve. In the construction shown in Figure 5 of the drawings, the outer surface of the metal sleeve II is always in engagement with the inner surface of the gasket II and consequently there is considerable friction therebetween which must be overcome by the coil compression spring II. The presence of this friction is avoided shortly after the movable terminal is released in the constructions shown in Figures 2 and 4 of the drawings.

Since certain further changes may be made in the above constructions and diiferent embodiments of the invention may be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed as new is:

l. A fuse link comprising, in combination, a pair of conductors in spaced relation interconnected by fusible means and protecting means for said fusible means including an outer sleeve of insulating material and a two part inner 1 sleeve, one part being formed of metal and the other part being formed of ceramic material, said parts being in end-to-end relation.

2. A fuse link comprising, in combination, a pair of conductors in spaced relation interconnected by fusible means, and protecting means for said fusible means including an outer sleeve of insulating material and an inner sleeve of ceramic material having a coating of are extinguishing material.

3. A fuse link comprising, in combination, a pair of conductors in spaced relation interconnected by fusible means, and protecting means for said fusible means including an outer sleeve of insulating material and an inner sleeve of ceramic material having a coating of boric acid.

4. A fuse link comprising, in combination, a pair of conductors in spaced relationinterconnected by fusible means, and protecting means for said fusible means including an outer sleeve of insulating material and an inner sleeve of ceramic material having a coating of magnesium borate.

5. A fuse link comprising, in combination, a pair of conductors in spaced relation interconnected by fusible means, protecting means for said fusible means including outer and inner sleeves of insulating material, said sleeves being biased for movement apart when said fusible means blows, and means for limiting said relative movement to prevent exposure of the resulting gap between said conductors.

6. A fuse link comprising, in combination, a pair of conductors in spaced relation interconnected by fusible means, protecting means for said fusible means including an outer sleeve of insulating material and a two part inner sleeve, one part being formed of metal and the other part being formed of insulating material, said sleeves being biased for relative movement apart when said fusible means blows, and means for limiting said relative movement in such manner as to place the part of said inner sleeve formed of insulating material around the resulting gap between said conductors.

7. In a circuit interrupter, in combination, a pair of relatively movable apart arcing terminals, an outer sleeve of insulating material and a relatively movable two part inner sleeve both surrounding said terminals, one part being formed of metal and the other part being formed of insulating material,.said terminals and said sleeves being biased for movement apart, and means for limiting said movement apart of said terminals and of said sleeves in such manner as to place the part of said inner sleeve formed of insulating material around the resulting gap between said terminals.

8. A fuse link for out of doors mounting and adapted to be directly exposed to the elements comprising, in combination, a pair of relatively movable apart relatively infusible terminals interconnected by fusible means, protecting means for said fusible means including an outer sleeve of weather-proof material adapted to evolve a pressure creating medium due to the heat of an are if the same is allowed to contact therewith, and a two-part inner sleeve between said outer sleeve and said fusible means, one part being formed of metaland the other part being formed of relatively inert insulating material, said sleeves being biased for relative movement apart when said fusible means blows, and means for limiting said relative movement in such manner as to place the part of said inner sleeve formed of relatively inert insulating material around the resulting gap between said terminals.

9. A fuse link for out of doors mounting and adapted to be directly exposed to the elements comprising, in combination, a pair of relatively movable apart relatively infusible terminals interconnected by fusible means, protecting means for said fusible means including an outer sleeve of weather-proof material, and a two-part inner sleeve between said outer sleeve and said fusible means, one part being formed of metal and the other part being formed of relatively inert insulating material, a coating of arc extinguishingcooled and condensed on said terminals and said' metal sleeve part, and means for limiting said relative movement in such manner as to place the 7 part of said inner sleeve formed of relatively inert insulating material around the resulting gap between said terminals.

'10. A fuse link comprising, in combination, a pair of relatively infusible terminals interconnected by fusible means and having flexible leads extending therefrom for connection to line conductors, means biasing said terminals for movement apart when said fusible means blows, a sleeve of insulation surrounding said terminals,

one of said terminals being fastened to said sleeve and the other being movable out of the same, the ends of said sleeve of insulation being substanntially sealed against the entrance of moisture, means limiting the outward movement of said other terminal whereby a mechanical but not electrical connection is maintained between said flexible leads to prevent dangling thereof after blowing of said fusible means, the resulting position of said other terminal indicating that the link has blown, and means substantially sealing the end of said sleeve of insulation against the entrance of moisture when the link is in the blown condition.

11. In a fuse link, in combination, a sleeve of insulating material, a terminal connected to a fusible element within said sleeve and movable out of one end of the same on blowing of said fusible element, and means limiting the movement of said terminal out of said sleeve, the end of said sleeve out of which said terminal moves being substantially sealed against the entrance of moisture in either the unblown or blown condition of the fuse link.

12. In a fuse link, in combination, a sleeve of insulating material, a terminal connected to a fusible element within said sleeve and movable out of one end of the same on blowing of said fusible element, a flange of limited width on said sleeve extending inwardly toward said terminal, and a gasket between said terminal and said flange providing a sealed connection therebetween, said terminal being freely movable relative to said sleeve as soon as said gasket is moved out of engagement with said flange.

13. In a fuse link, in combination, a sleeve of insulating material, a terminal connected to a fusible element within said sleeve and movable out of one end of the same on blowing of said fusible element, a flange of limited width on said sleeve extending inwardly toward said terminal, a gasket between said terminal and said flange providing a sealed connection therebetween, and a tube carried by said terminal and extending inwardly of said sleeve and having an outwardly extending flange at its inner end disposed to abut said flange on said sleeve for limiting outward movement of said terminal, said terminal being freely movable relative to said sleeve as soon as said gasket clears said flange on said sleeve until said flanges abut.

14. In a fuse link, in combination, a sleeve of insulating material, a terminal connected to a fusible element within said sleeve and movable out of one end of the same on blowing of said fusible element, a flange on said sleeve extending inwardly toward said terminal, a tube carried by said terminal and extending inwardly of said sleeve and having an outwardly extending flange at its inner end, and a gasket abutting the inner side of said flange on said sleeve and engaging said tube to provide a sealed connection therebetween, said terminal on blowing of said fusible element moving outwardly of said sleeve until said flange on said tube engages said gasket.

15. A fuse link comprising, in combination, a pair of conductors in spaced relation interconnected by fusible means, protecting means for said fusible means including an outer sleeve of insulating material and a two part inner sleeve, one part being formed of metal and the other part being formed of insulating material, and means for biasing said sleeves for relative movement when said fusible means blows to place the part of said inner sleeve formed of insulating material around the resulting gap between said conductors.

16. A fuse link comprising, in combination, a pair of conductors in spaced relation interconnected by fusible means, protecting means for said fusible means including an outer sleeve of insulating material and a two part inner sleeve,

one part being formed of metal and the other partbeing formedotinsulatingmaterial, anda coating of arc extinguishing material on said other part of said inner sleeve formed of insulating material.

17. A use link comprising, in combination, a pair of conductors in spaced relation interconnected by fusible means, and protecting means for said fusible means including an outer sleeve of insulating material and a two part inner sleeve, one part being formed of metal and the other part being formed of ceramic material hav- 5 ing a coating of arc extinguishing material.

SIGURD I. LINDEIL. ANTHONY VAN RYAN. 

